US4039763A - Key telephone communication path interface - Google Patents

Key telephone communication path interface Download PDF

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Publication number
US4039763A
US4039763A US05/709,421 US70942176A US4039763A US 4039763 A US4039763 A US 4039763A US 70942176 A US70942176 A US 70942176A US 4039763 A US4039763 A US 4039763A
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United States
Prior art keywords
circuit
line
impedance
communication
set forth
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Expired - Lifetime
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US05/709,421
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English (en)
Inventor
Ronald Joseph Angner
James Volney Lacy
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AT&T Corp
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Bell Telephone Laboratories Inc
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Publication date
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US05/709,421 priority Critical patent/US4039763A/en
Priority to CA283,135A priority patent/CA1083733A/fr
Priority to JP52089903A priority patent/JPS581876B2/ja
Application granted granted Critical
Publication of US4039763A publication Critical patent/US4039763A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M9/00—Arrangements for interconnection not involving centralised switching
    • H04M9/002—Arrangements for interconnection not involving centralised switching with subscriber controlled access to a line, i.e. key telephone systems
    • H04M9/005—Arrangements for interconnection not involving centralised switching with subscriber controlled access to a line, i.e. key telephone systems with subscriber controlled access to an exchange line
    • H04M9/006—Exchange line circuits

Definitions

  • This invention relates generally to an improved key telephone line circuit, and, more particularly, to a key telephone line circuit interface for use in parallel across the communication leads.
  • Shunt control has several advantages, but the most important one is the perfect balance of the tip and ring circuitry at all times. Other advantages include the ease of application of music and tone on hold signals and the fact that the circuit can be removed for maintenance in any state but HOLD or RING without disrupting customer service.
  • the shunt principle of HOLD/DISCONNECT detection is as follows: When a key station goes on-hook, two things happen sequentially:
  • the shunt line circuit must also operate to detect ringing and to provide a hold impedance across the communication pair when the line circuit is in the HOLD mode. Implicit in the ability of the line circuit to detect ringing signals is the ability to distinguish such signals from noise, TOUCH-TONE signals, dial pulses, or other unknown signal disturbances which periodically appear on telephone lines.
  • the line circuit impedance is always across the communication line in the IDLE, RING or BUSY modes there are a number of constraints that must be met in order for the line circuit to function properly.
  • the communication lead interface In the IDLE state the communication lead interface must not interfere with tests which are made by the Central Office (CO) or PBX. Such tests are routinely made to insure that at least one telephone ringer, and hence at least one telephone station, is connected to the line. Other tests are made to insure the proper insulation of the line.
  • CO Central Office
  • PBX Central Office
  • Such tests are routinely made to insure that at least one telephone ringer, and hence at least one telephone station, is connected to the line. Other tests are made to insure the proper insulation of the line.
  • care In the BUSY state care must be exercised to insure that the interface does not distort the signaling between the telephone station and the central switching machine and does not adversely affect the voice transmission over the communication pair.
  • a key telephone line circuit having a communication path interface circuit capable of permanent connection across the communication path and capable of satisfying the precommunication period restraints as well as the communication period restraints.
  • a varistor is used, coupled with Light Emitting Diodes (LEDs), to provide an impedance which consists essentially of a series combination of resistance and capacitance at low amplitude signals.
  • LEDs Light Emitting Diodes
  • the impedance which consists essentially of a series combination of resistance and capacitance at low amplitude signals.
  • the LEDs begin to conduct lowering the impedance presented to the line circuit and introducing nonlinearity into the circuit. The effect becomes even more pronounced when the varistor begins to conduct during most of a ringing cycle or other ac cycle.
  • the impedance approaches that of the series capacitor and resistor.
  • a key telephone line circuit is arranged with series capacitance and resistance elements coupled to the line via nonlinear circuit elements in a manner which satisfies the ring test, impedance test and circuit communication requirements while also remaining on the communication path during the active communication condition of the connection.
  • a key telephone line circuit is arranged for permanent connection across the communication pair by a combination of linear and nonlinear circuit elements, the combination of elements combining to provide essential transparency to voice and signal communication over the communication pair while also serving to detect circuit status signal information transmitted over the communication pair.
  • control circuit IC1 The line circuit shown in the drawing is designed for operation with a control circuit shown as control circuit IC1.
  • control circuit IC1 The details of the operation of control circuit IC1 are set out in concurrently filed copending application of R. J. Angner et al, Ser. No. 708,857, (Angner 15-1-4) and in the interest of economy will not be repeated herein.
  • the aforementioned Angner, Blount, Lacy application is hereby incorporated herein and made a part hereof as though fully reproduced.
  • the impedance of the tip-ring interface in the line circuit is both frequency and amplitude dependent and, in general, is nonlinear.
  • the disclosed line circuit communication path interface is across the communication line when the line circuit is in the IDLE, RING, and BUSY states; the tip-ring detector is not switched out in the BUSY state as in the past.
  • the total impedance across the line is simply the series impedance of capacitor 1C1 (approximately 1.1 ⁇ f) and resistors 1R2 (approximately 7.5K ohms), and 1R3 (approximately 3.83K ohms).
  • capacitor 1C1 approximately 1.1 ⁇ f
  • resistors 1R2 approximately 7.5K ohms
  • 1R3 approximately 3.83K ohms
  • the line circuit In the IDLE and RING states, the line circuit must present a load to the communication line which appears as a telephone ringer to the switching machine. This is necessary to satisfy the impedance test which is satisfied by a 600 ohm load to an ac signal or a 200 ohm load to a dc signal. In systems with common audible signaling, the line circuit load substitutes for the load of actual ringers across the line. Since a simple series R-C circuit is used to replace the prior art R-L-C network, care was taken to choose the component values to insure that all COs and PBXs will interpret the load correctly under all normal line conditions.
  • the ringing current flow test is performed by COs and PBXs to test for the presence of a ringer (and therefore a telephone set) on the line during the application of CO ringing.
  • a ringer and therefore a telephone set
  • the impedance of the ring detector must be low enough to cause sufficient ac loop current to flow to trip a current sensing circuit at the switching machine. This requirement is met since the communication line interface presents to the ringing generator a maximum impedance of 11.3 at an angle of -40.0° kilohms and will therefore source a minimum current of 6.6 milliaperes RMS at 75 volts RMS, 20 Hertz.
  • the line status verification test is made to check for the presence of a telephone ringer bridged across the line.
  • the ring detector in the line circuit may substitute for a true ringer in some key systems.
  • the test equipment applies a low amplitude ac signal to the line and monitors the current waveform. It will recognize the series R-C termination of a ring detector as a ringer if the effective dynamic resistance of the circuit falls within 6500 to 13000 ohms for values of capacitance greater than 1.05 microfarads.
  • Presently designed equipment applies a signal which may not have sufficient amplitude to cause varistor 1V1 or the LEDs in optical isolator shunt detector 103 to conduct.
  • the effective resistance is resistor 1R2 and 1R3 in series. If the amplitude of the applied signal is increased, causing nonlinear devices 1D1, 1D2 in shunt detector 103 to conduct, resistor 1R3 is shunted causing the dynamic resistance across the communication paths to decrease, but it always remains within the limits specified above.
  • the impedance of the line circuit ring detector is greater than that of a typical telephone ringer at 20 and 30 Hertz, and that the use of the line ring detector does not present a problem in regard to ringing pretrip or range.
  • the ring detector Since the ring detector is not disconnected from the line in the BUSY state, it will contribute to dial pulse distortion in much the same way that ringers do. In general, increasing the series capacitance of a ringer or ring detector decreases the percent break of the dial pulses and increasing the series resistance increases the percent break. Typical ringers have a total series resistance of 3650 ohms and require a 0.45 microfarad series capacitor in contrast to the 7500 ohms and the 1.1 microfarads for the disclosed line circuit. The amplitude of the dial pulses is quite large compared to the forward voltage characteristics of varistor 1V1 and the LEDs in shunt detector 103, so that resistor 1R2 and capacitor 1C1 are the dominant elements in the line circuit. Since the higher capacitance and resistance of the ring detector tend to compensate for each other, the bridged ring detector does not cause significantly more dial pulse distortion than does a true ringer.
  • the maximum level per frequency pair for multifrequency signals is +4 dbm, which corresponds to 1.5 volts RMS into 900 ohms, which is below the signal level that will cause varistor 1V1 or the LEDs in shunt detector 103 to conduct significant current, as compared to resistor 1R2. Consequently, the additional load presented to the multifrequency generator is linear and consists of capacitor 1C1 in series with resistors 1R2 and 1R3.
  • the line circuit must be capable of ringing up on as low as 40 volts RMS, 20 or 30 Hertz ringing signals if it is to be compatible with all COs, PBXs, and range extenders on standard, ungauge and extended loops.
  • the line circuit should not ring up when nonringing signals are present on the line.
  • a line circuit When a line circuit is in the IDLE and RING states, it may be exposed to any of the following types of signals or noise: (1) dial pulsing generated by a station without A-lead control; (2) TOUCH-TONE signals generated by stations without A-lead control; (3) CO battery interruptions or reversals (4) hum pick-up from power lines and other sources of 60 Hertz radiation; and (5) crosstalk from other wires in telephone cables.
  • the sensitivity of the shunt detector determines the signal amplitude, waveform, and frequency required to generate a continuous logical 1 at the DIN input;
  • ring-up delay timing in the IDLE and RING states requires a continuous logical 1 at the DIN input for at least 170 milliseconds to generate a transition from the IDLE to RING state; and once in the RING state, DIN must remain high for at least 110 milliseconds to reset the ring time-out timer.
  • the line circuit will not ring up in response to dial pulsing, battery interruptions, or battery reversals.
  • the maximum level per frequency pair for a multifrequency signal is +4 dbm, which corresponds to 1.5 volts RMS into 900 ohms, which is well below the signal level required to cause the line circuit to ring up.
  • capacitor 1C1 charges to the average dc voltage across the line. Should the voltage across the line change for any reason, current flows through shunt detector 103, charging capacitor 1C1 to the new line voltage. If the voltage change is large enough and fast enough, the charging current generates a voltage drop across the LEDs in shunt detector 103 of sufficient amplitude to cause them to conduct enough current to turn phototransistors 1Q1 and 1Q2 on, thus generating a pulse at the DIN output. Note that antiparallel LEDs 1D1 and 1D2 allow detection of positive-going and negative-going transitions with either polarity of the battery supply.
  • the shunt line detector has been designed to generate a pulse of at least 1.0 milliseconds in response to a 6.0 volt step change in voltage across the line. This high a sensitivity is more than adequate for standard, uniguage, and extended loop lengths of zero to maximum length where the only additional devices bridged across the line are ringers and/or key telephone line circuits.
  • the minimum sensitivity of the shunt detector has been set at 6.0 volts in order to respond correctly to switchhook flashes when operating in conjunction with PBXs.
  • relay H When the line circuit is in the HOLD state, relay H is energized completing a path for loop current to flow through hold bridge resistor 1R1 (120 ohms) via enabled make contact H-1, and the parallel combination of resistor 1R3, varistor 1V1, and LEDs 1D1 and 1D2 in shunt detector 103 in series with resistor 1R4. Most of the hold bridge current flows through varistor 1V1 (equivalent to 3 diode drops in either direction) which limits the maximum current that flows through the LEDs in the optical isolator shunt detector. Resistor 1R4 permits 1 to 5 milliamperes to flow through the LEDs when the circuit is in the HOLD state.
  • the phototransistor is saturated, providing a steady logical 1 indication at the DIN input. If CO battery is interrupted, the hold bridge current drops to zero, the LEDs stop conducting, and the DIN input to control circuit IC1 goes to logical 0.
  • the minimum hold bridge current which will cause the voltage at the DIN input to go high can range from 0.25 to 0.60 milliamperes, largely because of variations in the current transfer ratio of shunt detector 103.

Landscapes

  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Sub-Exchange Stations And Push- Button Telephones (AREA)
  • Interface Circuits In Exchanges (AREA)
  • Monitoring And Testing Of Exchanges (AREA)
US05/709,421 1976-07-28 1976-07-28 Key telephone communication path interface Expired - Lifetime US4039763A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US05/709,421 US4039763A (en) 1976-07-28 1976-07-28 Key telephone communication path interface
CA283,135A CA1083733A (fr) 1976-07-28 1977-07-20 Interface de trajets pour systeme telephonique a clavier
JP52089903A JPS581876B2 (ja) 1976-07-28 1977-07-28 ライン回路

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US05/709,421 US4039763A (en) 1976-07-28 1976-07-28 Key telephone communication path interface

Publications (1)

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US4039763A true US4039763A (en) 1977-08-02

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US05/709,421 Expired - Lifetime US4039763A (en) 1976-07-28 1976-07-28 Key telephone communication path interface

Country Status (3)

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US (1) US4039763A (fr)
JP (1) JPS581876B2 (fr)
CA (1) CA1083733A (fr)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4101741A (en) * 1977-03-14 1978-07-18 International Standard Electric Corporation Line circuit for key telephone systems
US4101740A (en) * 1977-03-14 1978-07-18 International Standard Electric Corporation Line circuit for key telephone systems
US4194093A (en) * 1978-11-29 1980-03-18 International Telephone And Telegraph Corporation Key system protective apparatus
US4207439A (en) * 1978-07-13 1980-06-10 International Telephone And Telegraph Corporation Line/interface circuit for key telephone systems
US4323735A (en) * 1980-09-26 1982-04-06 Bell Telephone Laboratories, Inc. Key telephone line shunt detector circuit
US4758920A (en) * 1987-03-02 1988-07-19 Oneac Corporation Telephone and data overvoltage protection apparatus
US4941063A (en) * 1988-03-04 1990-07-10 Oneac Corporation Telephone lines overvoltage protection apparatus
US5357568A (en) * 1992-06-08 1994-10-18 Oneac Corporation Telephone line overvoltage protection method and apparatus
US5699218A (en) * 1996-01-02 1997-12-16 Kadah; Andrew S. Solid state/electromechanical hybrid relay
US5905623A (en) * 1997-05-27 1999-05-18 Oneac Corporation Telephone and data overvoltage protection apparatus including a longitudinal transformer
US6266223B1 (en) 1999-06-30 2001-07-24 Tyco Electronics Corporation Line protector for a communications circuit
US20140185791A1 (en) * 2012-12-27 2014-07-03 Canon Kabushiki Kaisha Apparatus and control method for the same

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3816670A (en) * 1972-12-26 1974-06-11 Gte Automatic Electric Lab Inc Line card circuit for a key telephone system
US3856994A (en) * 1973-07-13 1974-12-24 Basic Inc Key telephone unit line card
US3895192A (en) * 1974-07-25 1975-07-15 Bell Telephone Labor Inc Telephone line circuit hold control arrangement
US3925625A (en) * 1974-07-25 1975-12-09 Bell Telephone Labor Inc Transient controlled telephone line circuit
US3946146A (en) * 1975-01-17 1976-03-23 Gte Automatic Electric Laboratories Incorporated Discrete ringing detector for use in key telephone systems

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5344883Y2 (fr) * 1974-02-20 1978-10-27
JPS5120606A (ja) * 1974-08-13 1976-02-19 Taiko Electric Works Ltd Botandenwasochi

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3816670A (en) * 1972-12-26 1974-06-11 Gte Automatic Electric Lab Inc Line card circuit for a key telephone system
US3856994A (en) * 1973-07-13 1974-12-24 Basic Inc Key telephone unit line card
US3895192A (en) * 1974-07-25 1975-07-15 Bell Telephone Labor Inc Telephone line circuit hold control arrangement
US3925625A (en) * 1974-07-25 1975-12-09 Bell Telephone Labor Inc Transient controlled telephone line circuit
US3946146A (en) * 1975-01-17 1976-03-23 Gte Automatic Electric Laboratories Incorporated Discrete ringing detector for use in key telephone systems

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4101741A (en) * 1977-03-14 1978-07-18 International Standard Electric Corporation Line circuit for key telephone systems
US4101740A (en) * 1977-03-14 1978-07-18 International Standard Electric Corporation Line circuit for key telephone systems
US4207439A (en) * 1978-07-13 1980-06-10 International Telephone And Telegraph Corporation Line/interface circuit for key telephone systems
US4194093A (en) * 1978-11-29 1980-03-18 International Telephone And Telegraph Corporation Key system protective apparatus
US4323735A (en) * 1980-09-26 1982-04-06 Bell Telephone Laboratories, Inc. Key telephone line shunt detector circuit
US4758920A (en) * 1987-03-02 1988-07-19 Oneac Corporation Telephone and data overvoltage protection apparatus
US4941063A (en) * 1988-03-04 1990-07-10 Oneac Corporation Telephone lines overvoltage protection apparatus
US5357568A (en) * 1992-06-08 1994-10-18 Oneac Corporation Telephone line overvoltage protection method and apparatus
US5699218A (en) * 1996-01-02 1997-12-16 Kadah; Andrew S. Solid state/electromechanical hybrid relay
US5905623A (en) * 1997-05-27 1999-05-18 Oneac Corporation Telephone and data overvoltage protection apparatus including a longitudinal transformer
US6266223B1 (en) 1999-06-30 2001-07-24 Tyco Electronics Corporation Line protector for a communications circuit
US20140185791A1 (en) * 2012-12-27 2014-07-03 Canon Kabushiki Kaisha Apparatus and control method for the same
US9300788B2 (en) * 2012-12-27 2016-03-29 Canon Kabushiki Kaisha Apparatus and control method for the same

Also Published As

Publication number Publication date
CA1083733A (fr) 1980-08-12
JPS5317008A (en) 1978-02-16
JPS581876B2 (ja) 1983-01-13

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